1. Field of the Invention
The invention relates to a sustained release dispenser as well as a pest control method, enabling a simultaneous release of two or more sex pheromone substances.
2. Description of the Related Art
As an effective method for utilizing a sex pheromone of an insect pest, the method has progressed to a practical stage, where a certain concentration of chemically synthesized sex pheromone is kept in a field so as to disrupt the mating of the insect pest. The important issues for the pest control method are development of the sustained release formulation (or dispenser) which can discharge a synthesized sex pheromone substance of an insect pest at a certain rate or higher in a long period; and the period of the mating disruption toward a target insect pest.
There are many cases where it is relatively easy to control the release of one or more sex pheromone substances of a single species of insect pest at a certain rate in a certain period because said one or more sex pheromone substances are only one kind or two or more substances having similar chemical structures. However, it is difficult to enclose sex pheromone substances with very different chemical structures in one dispenser and then control the release of the substances toward an insect pest having the substances. For instance, a diamondback moth (Plutella xylostella), an insect harmful to vegetables, has the sex pheromone substances (Z)-1′-hexadecenal and (Z)-hexadecenyl acetate; and the beet armyworm (Spodoptera exigua (Hubner)(Lepidoptera: Noctudae)), an insect harmful to vegetables, has the sex pheromone substances (Z, E)-9, 12-tetradecenyl acetate and (Z)-9-tetradecenol. Thus, each harmful insect has sex pheromone substances with different functional groups. Further, a principal component in the sex pheromone substance of leaf rollers, insects harmful to fruit trees and tea, is (Z)-11-tetradecenyl acetate and some of minor components therein are (Z)-9-dodecenyl acetate and 11-dodecenyl acetate. Thus, although the components have same functional groups, they have different carbon numbers. Hence, when the components are enclosed in a same dispenser, it is not possible to control the release of each component because of each component having different vapor pressure. It should be noted that there is rarely a single kind of insect pest for a certain crop. Thus, it is usually necessary to control two or more insect pests simultaneously in an area having various insect pests such as Japan.
The difficulties encountered when designing a sustained release dispenser which releases compounds having different chemical structures simultaneously are described below:                (1) The release of compounds cannot be controlled because of each compound having a different boiling point (vapor pressure) due to a different functional group thereof;        (2) The release of compounds cannot be controlled because of each compound having a different boiling point (vapor pressure) due to a different carbon number thereof, even when the functional group of each compound is identical;        (3) A dispenser comprising a porous support without a vapor barrier will release a compound having a higher vapor pressure faster even if an evaporation area is identical.        
It is also difficult to design a sustained release dispenser toward two or more insects at the same because the generation period of each insect pest differs.